1. Field of the Invention
The present invention relates to a method of measuring and controlling a concentration of dopants of a thin film in a process of manufacturing a semiconductor device. More particularly, the present invention relates to a method of measuring and controlling a concentration of dopants of a thin film using X-ray fluorescence spectroscopy.
2. Description of the Related Art
Recently, electronic apparatuses have become small in size and light in weight. A semiconductor device is essential to electronic apparatuses. Dopants are injected into an intrinsic semiconductor, so that a semiconductor device is manufactured. When dopants having three valence electrons are injected into an intrinsic semiconductor having four valence electrons, one of the four valence electrons is not paired, so that an acceptor is formed. When dopants having five valence electrons are injected into the intrinsic semiconductor having four valence electrons, one of the five valence electrons remains, so that a donor is formed. When the acceptor or the donor moves due to a difference of voltage, current flows. Therefore, electric characteristics of semiconductor devices are related to a concentration of dopants.
An amorphous silicon layer or a polysilicon layer into which dopants are injected is used for a capacitor or a transistor. Phosphorous (P) may be used as the dopant.
In a conventional method for injecting dopants, an amorphous silicon layer or a polysilicon layer is deposited on a substrate first, and then dopants such as phosphorous are injected into the amorphous silicon layer or the polysilicon layer via a POCl3 process.
More recently, an amorphous silicon layer or a polysilicon layer including dopants, such as phosphorous, is deposited directly onto the substrate.
The concentration of dopants may be measured using X-Ray Fluorescence (XRF) or Secondary Ion Mass Spectroscopy (SIMS). SIMS is very sensitive to a surface condition of the amorphous silicon layer or of the polysilicon layer. Further, SIMS is an intrinsically destructive method of measuring the concentration of dopants. Therefore, X-ray fluorescence, which is a characteristic X-ray, is more frequently used for measuring a concentration of dopants.
In a conventional method of measuring concentration of dopants, light having a specific wavelength range is irradiated onto a thin film including dopants. Then, optical characteristics such as refractivity, an absorption ratio or a reflection ratio are measured to analyze the concentration of the dopants. In detail, a thin film having a specific concentration of dopants is deposited on a wafer that is not patterned, so that a criterion wafer is formed. The optical characteristics of the thin film deposited on the criterion wafer, such as the refractivity, the absorption ratio or the reflection ratio, are measured. A correlation between the specific concentration of dopants and the optical characteristics is induced. Then, the optical characteristics of an objective thin film deposited on a wafer that is patterned are measured. Measured data of the objective thin film are compared with the correlation, so that the concentration of the dopants of the objective thin film is obtained.
However, the method described above requires use of the criterion wafer. The criterion wafer that is not patterned is specially manufactured to reflect a real wafer that is patterned.
In a conventional semiconductor device manufacturing process, a plurality of thin films including dopants is deposited and patterned in sequence. When the concentration of dopants of each thin film is measured using the criterion wafer, a plurality of the criterion wafers corresponding to each of the thin films is required. Each criterion wafer is costly to manufacture in both expense and time, and therefore, productivity is low.
Furthermore, a significant amount of time is needed to measure the concentration of dopants. Therefore, when defects of the concentration of dopants are detected, a large number of wafers manufactured during a measuring time are wasted.